Plastic pellet delivery system

ABSTRACT

A plastic pellet delivery system including an extruder nozzle having an orifice and an arcuate surface adjacent the orifice and rigid cutting knife which is eccentrically mounted on a shaft that is positioned and is rotated adjacent the orifice to move the rigid knife eccentrically into and out of engagement with the nozzle surface. The cutting knife is mounted for limited yielding pivotal movement relative to the eccentric mount such that it will deflect angularly with respect to the eccentric mount as it is engaging the nozzle surface such that the free edge of the knife blade tip is moved radially inwardly as the eccentric mount is rotated providing a substantially constant force of the blade against the nozzle surface.

This is a continuation of application Ser. No. 08/095,463, filed on Jul.22, 1993, and now U.S. Pat. No. 5,386,971.

This invention is related to plastic pellet delivery systems andparticularly to such systems for delivering a predetermined precisequantity of plastic for use in compression molding plastic closures andcompression molding liners in plastic closures.

BACKGROUND AND SUMMARY OF THE INVENTION

In the manufacture of plastic closures by compression molding and theprovision of liners in plastic closures, it is common to utilize pelletdelivery systems. Typical patents showing such systems are: U.S. Pat.Nos. 2,640,033, 3,458,897, 3,676,029, 3,828,637, 3,955,605, 4,080,136,4,157,048, 4,269,584, 4,277,431, 4,440,704, 4,800,792 and 4,978,288.

In one type of system which has been used as shown in U.S. Pat. Nos.4,080,136 and 4,277,431, a flexible and resilient blade is moved along asurface surrounding the extrusion nozzle and after it moves past thesurface snaps to accelerate the pellet to the place of use. It has beenfound that such a system is difficult to set up and requires substantialattention. Furthermore, it requires frequent adjustment. In addition, ithas limited life and must be replaced rather frequently.

Accordingly among the objectives of the present invention are to providea pellet delivery system that is less dependent upon operating skill,needs less attention, utilizes a construction that has longer life;provides better alignment of a cutting knife blade with respect to theextrusion orifice, and provides for better control and placement of thepellet.

In accordance with the invention a plastic pellet delivery systemincluding an extruder nozzle having an orifice and an arcuate surfaceadjacent the orifice and rigid cutting knife which is eccentricallymounted on a shaft that is positioned and is rotated adjacent theorifice to move the rigid knife eccentrically into and out of engagementwith the nozzle surface. The cutting knife is mounted for limitedyielding pivotal movement relative to the eccentric such that it willdeflect angularly with respect to the eccentric mount as it is engagingthe nozzle surface such that the free edge of the knife blade tip ismoved radially inwardly as the eccentric mount is rotated providing asubstantially constant force of the blade against the nozzle surface.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a pellet delivery system embodying theinvention.

FIG. 2 is a part sectional plan view thereof.

FIG. 3 is a part sectional end view thereof.

FIG. 4 is a fragmentary part sectional partly diagrammatic end view of aportion of the apparatus.

FIG. 5 is a fragmentary part sectional end view of a modified form ofapparatus.

DESCRIPTION

Referring to FIG. 1, the pellet delivery system comprises a cutterassembly 20 that is mounted by the parallel links 21 of a parallelogramlinkage which are pivoted to the cutter 20 and a base 22. A fluidcylinder 23 extends between the base 22 and one of the links 21 to movethe cutter assembly to and from position. Stops 24, 25 are provided forcontrolling the movement in each direction. Each stop 24, 25 includes ashock absorber.

Referring to FIGS. 2-4, the cutter delivery assembly 20 includes a servomotor 26 that drives a shaft 27 supported by bearings 28, 29 torotatably mount a removable blade holder 30. The blade holder 30 ismounted on shaft 27 by an integral shaft 31 that has an end formed witha radial key that engages a complementary key in the shaft 27. The shaft31 is locked to shaft 27 by a collet 32 on shaft 27 that has a colletnut 33 threaded thereon.

The blade holder 30 has a hole 34 bored eccentrically to receive a pivotpost 35 which, in turn has a slot 35a for receiving a rigid cutter bladeor knife 36. The blade 36 has limited circumferential movement, beingyieldingly urged in the direction of rotation by spaced plungers 37 thatare urged toward the blade by springs 38 mounted in a bracket 39 suchthat the blade 36 is held against a stop surface on the pivot bladeholder 30. The cutter blade 36 is adapted to move past a nozzle block 40through which extrudate such as plastic material is directed out of anozzle 41. The slot 35a on the pivot post 35 extends axially and has aflat side 42 and an opposed side 43 with an integral axial rib 44. Thecutter blade 36 has an inner end with a complementary cross section thatis slightly smaller to limit circumferential movement of the cutterblade 36. This cross section includes a flat side 45 and an opposed side46 having an axial groove 47.

As the blade holder 30 rotates the free edge 36a of the cutter blade 36is projected substantially radially onto the arcuate concave surface 41aof the nozzle 41 and is deflected angularly with respect to the bladeholder 30 in a direction counter to the direction of rotation therebyproviding a substantially constant force of the blade 36 against thenozzle surface 41a. As the blade 36 moves across the nozzle orifice 41,a pellet of extrudate is severed from the nozzle 41 and then uponfurther rotation of the blade holder 30 the free edge 36a of the blade36 moves past the surface 41a and the yieldingly force of the plungers37 deflect the pellet toward the work station, in this case a mold orthe interior of a closure (not shown).

In the form shown in FIG. 5, the yielding force on the blade 36b isprovided by a flat spring 50 engaging the surface of the blade.

The axis of rotation of the shaft 27 and the blade holder 30 areadjustably displaced from the arc center of the cylindrical surface 41aof the nozzle block 41.

The blade 36 and pivot post 35 could, alternatively, be manufactured asone piece, and in the shape of a key hole in cross section. The circularsection of the post would function as the blade shaft forming thepivoting point of the blade.

The pivot post 35 is eccentrically mounted on the blade holder 30 in theorder of 0.150 in., being housed in a bore within, and eccentric to theaxis of rotation of the blade holder 30.

The two plungers 37 actuated by compression springs function on theblade 36 to preload the rotation of the blade 36 in the same directionas the rotation of the blade 36 for cutting and holding the blade 36against a mechanical stop on the blade holder 30. Thus the blade 36 canbe pivoted about the center of the pivot post 35 in a direction oppositethe rotation for cutting, only by compressing the springs 38.

The drive shaft 27 is bearing mounted and driven by the servo motor 26at a rotational speed proportional to the rate of delivery of the moldor closure to which the pellet is delivered.

Relative sliding movement of the cutter assembly 20 to the nozzleassembly 52 is provided in order to clear the cutter 36 from theextrudate while extruding material during set up and while not rotatingthe cutter. Also relative movement of the whole cutter assembly andnozzle assembly to the machine frame is provided such that extrudate canexit the nozzle 41 and fall to a collecting area away from the capdelivery means.

Operation

The cutter drive shaft 27 is driven at a rotational speed proportionalto the rate of delivery of the molds or caps. The extrudate is allowedto stabilize at a controlled delivery rate proportional to the rate ofdelivery of the molds or caps. The nozzle is then moved to engage theblade 36 with the nozzle 41, and its position is fixed by the adjustmentscrew 51 such that the normal path of the blade tip would cause aninterference with the nozzle of about 0.015 in., for example.

The nozzle 41 has a generally cylindrical surface, and has a tangentialsurface portion 41a at the entry position of the cutter blade 36 toallow for the entry of the blade 36. As the blade 36 contacts the entryarea of the nozzle 41, the tip 36a of the blade 36 is held back byfriction, and as the drive shaft 27 continues to rotate, the blade 36pivots within its eccentric bushing in a direction relatively oppositethat of the cutter shaft rotation and in opposition to the springs 38.This action causes the blade tip 36a to move in toward the center of thedrive shaft 27, and this in turn results in an effective reduction inthe arc radius subscribed by the blade tip 36a, until the subscribed arcmatches the generally cylindrical surface 41a of the nozzle 40. If thegenerally cylindrical surface 41a of the nozzle 41 is not exactlyconcentric to the axis of the cutter drive shaft 27, then the tip 36a ofthe blade 36 accommodates this variation by pivoting of the blade 36 ineither the direction of rotation under spring pressure or in the reversedirection by the action of friction with the nozzle.

When the cutting is complete, and the cutter blade 36 leaves the nozzle41, the plungers 34 extend, and cause a "flip" action to the blade 36which helps to release the pellet from the blade 36.

When the cutting action is stabilized, the whole cutter and nozzleassembly is moved in toward the cap delivery system, and the pellets aredirected into the moving cap in preparation for molding.

It can thus be seen the pellet delivery system provides a pellet cuttingknife 36 that engages and transverses a nozzle from which a continuousstream of extrudate is being supplied from an extruder and/or pump andthereby cleanly cut the extrudate into individual pellets withoutstringing the material. In order to avoid fatigue breakage or weakeningof the blade, it is desirable to use a blade of solid construction, andthis necessitates a means to ensure that the blade can slide over thenozzle surface and yet maintain a minimum, controlled interference withthe nozzle. To achieve this, the blade is mounted on an axis which iseccentric to the axis of the drive shaft, such that any pivoting of thesolid blade about its own axis will displace the tip of the blade,relative to the centerline of the drive axis, in a radial direction. Toestablish a primary position of the blade relative to the drive axis,and further to provide resilience against (pivoting) deflection of theblade about its mounting axis, a spring means is used to act as atorsional bias to the blade.

By choice of geometry, the apparatus automatically compensates forcutter wear, and for variability in the setting of the drive axisrelative to the nozzle (cutter engagement). Deflection of the cutter asit engages the nozzle and the simultaneous radially inward movement ofthe blade tip ensures a substantially consistent force of the bladeagainst the nozzle, for varying amount of adjustment of the drive shaftdisplacement from the nozzle and/or blade tip wear.

Compared to a flexible steel blade, the present apparatus has thefollowing advantages:

1) Rigid blade is less susceptible to breakage, and will not fatigue.

2) Device is less dependent upon operator skill in setting the device,and needs less attention.

3) Rigid blade can be manufactured from any of several material choicesto suit application.

4) Consistent blade engagement independent of cutter engagement setting.

5) More substantial mounting than flexible blade, having betteralignment to nozzle.

6) Better control of pellet placement due to less variability in bladeengagement.

7) Means to continually compensate for variance in the radius of the arcswept by the tip of a rigid blade as the tip contacts a substantiallycylindrical surface. This variance being a result of axis displacementof the cutter drive shaft from the said cylindrical surface, oreccentricity of the cylindrical surface to the axis of rotation orundulations in the cylindrical surface.

I claim:
 1. A pellet delivery system comprisingan extruder nozzlecomprising a body having an orifice through which an extrudate isdelivered and an arcuate concave substantially cylindrical surfaceintersected by said orifice, a rigid cutting knife having a free edge, arotating shaft rotatable about an axis parallel to the axis of thecylindrical surface, means for mounting said rigid cutting knife on saidshaft such that a free edge of said cutting blade is moved past saidorifice surface and engages said surface, said means for mounting saidrigid cutting knife being such that said knife has limited angularmovement circumferentially along its free edge which engages saidsurface, said means for mounting said cutting knife including meansyieldingly urging said cutting knife in a direction corresponding to thedirection of rotation of said shaft such that when said shaft isrotated, said surface is engaged by the free edge of the cutting knife,the cutting knife is deflected angularly with respect to said shaft inthe direction opposite to the direction of rotation and the free edgemoves radially inwardly to conform to the arcuate cylindrical surfaceand sever a pellet from the extrudate, said means for mounting saidcutting knife comprising a blade holder mounted on said shaft and havinga slot for receiving said rigid cutting knife, means for providinglimited angular movement of said knife circumferentially.
 2. The pelletdelivery system set forth in claim 1 wherein said means yieldinglyurging said cutting knife circumferentially comprising spaced plungersand springs associated by said plungers and urging said plungers intocontact with said knife.
 3. The pellet delivery system set forth inclaim 1 wherein said means yieldingly urging said cutting knifecircumferentially comprises a flat opening engaging a surface of saidknife.
 4. The pellet delivery system set forth in claim 1 including anintegral shaft supporting said blade holder and means locking integralshaft to said rotating shaft.
 5. The pellet delivery system set forth inclaim 4 wherein said means locking said integral shaft comprises acollet on the rotating shaft and a collet next threaded on said rotatingshaft.
 6. The pellet delivery system set forth in claim 1 wherein saidblade holder includes a pivot post having said slot therein.
 7. Thepellet delivery system set forth in claim 6 wherein said pivot post hasan axial rib along one surface of said slot, said knife having an axialgroove engaging said rib.
 8. The pellet delivery system set forth in anyone of claims 1-7 including a servo motor driving said rotating shaft.9. The pellet delivery system set forth in claim 8 wherein said rotatingshaft, cutting knife means for mounting said knife on said shaft andsaid servo motor comprises a cutter assembly and means for moving saidcutter assembly toward and away from said extruder nozzle.